This invention relates to a skived and hemmed blank construction, and to a method and an apparatus exhibiting particular utility in the treatment of paperboard blanks and webs to render them more useful for packaging.
Paperboard containers are widely used for the packaging of foodstuffs such as powdered mixes, cereals, corn chips and the like and are suitable for packaging liquids in general and many non-food substances, particularly those which are moisture-sensitive. Such containers are often formed from precut blanks comprising paperboard covered on both surfaces with a thermoplastic material such as polyethylene. The polyethylene inhibits passage through the paperboard of bacteria and other microorganisms, moisture, and the contents of the container. Additionally, the thermoplastic coating serves as an adhesive when subjected to heat and pressure. Thus, seams or joints between overlapped edges of the blank may be made by applying heat and pressure to the overlapped edges. The laminate also frequently includes a layer of metal foil (e.g., aluminum) to make the material relatively impervious to oxygen.
The sequence of operations for producing a paperboard container of this kind is as follows. A laminate comprising paperboard covered on both surfaces with a thermoplastic material, such as polyethylene, is formed in webs of indefinite lengths. Blanks of a desired size and shape are then cut out from the webs. The blanks are shipped to a packaging plant, where they are folded or wrapped by automatic machinery to form a tube which typically is provided with an end closure. The containers thus formed are then filled with a product by means of automatic filling apparatus after which a closure is affixed to the open end of each container.
After the blank has been formed and seamed into a tube, one edge of the blank, at the tube seam, is located inside the container (hereinafter "the inside edge"). If the inside edge is raw or exposed, the paperboard layer will come into contact with the contents of the container. Such contact is undesirable because any liquid in the container will wick into the cut or raw edge of the blank, and enter the paperboard component of the laminate. In addition, if a raw, cut edge of the blank is on the outside of the container, the paperboard may absorb moisture or bacteria and other microorganisms at the raw edge. If the laminate includes a foil layer to make the container oxygentight, the raw inside edge is also a problem because it provides a path by which atmospheric oxygen can easily enter the container.
A variety of blank constructions and methods of forming or treating blanks have been developed in an attempt to overcome these problems. Several examples of such prior constructions and methods are disclosed in U.S. Pat. Nos. 1,200,803 (Besozzi), 3,058,868 (Schroeder), 3,401,608 (Labombarde), 3,456,863 (Mollison), 3,495,507 (Haas), 3,604,317 (Baun), 3,604,613 (Haas), 3,654,842 (Schwenk), 3,716,435 (Jensen), 3,770,540 (Fuchs), 3,846,220 (Buchner), 4,239,150 (Schadowski et al.) and 4,254,693 (Schadowski et al.), and in U.K. Pat. No. 1,122,346.
One approach to solve the problem of such exposed edges involves removing a portion of the thickness of the laminate along the edge in question and folding the thinned portion in such a manner as to cover the exposed paperboard. This expedient is exemplified by the disclosures of U.S. Pat. Nos. 3,058,868, 3,495,507 and 3,604,317. If the thinned portion is merely folded over itself, a paperboard-paperboard bond must be made to hold the folded-down portion in place. An adhesive is usually necessary for such a bond, requiring an additional manufacturing step (unless the folded portion is held in place by means of the side seam of the final container, which requires that the blank be made into a container immediately). Alternatively, the folded-over portion can be secured to the thermoplastic layer adjacent the cut. This, however, increases the thickness of the blank at the edge in question, requiring additional space for shipping and storage. As mentioned, the blank can be formed into a container before shipment, but the manufacturer of the blanks is ordinarily not the company that fills the containers, and shipping empty containers is highly uneconomical.
The problem of uneven blank thickness can be mitigated by ironing the folded-over portion into the thermoplastic layer to which it is bonded, as disclosed in U.S. Pat. No. 3,604,317. Even with this expedient, however, another problem is encountered in obtaining a good seal when closing the filled container. Because the container side wall has a double thickness of material at the side seam, an exactly circular end closure will not fit perfectly over the end of the container but will leave a small hole adjacent the double thickness. This hole must somehow be closed to achieve a fully reliable seal. This problem is compounded if the end of the container side wall is curled, since the double thickness makes the rim of the container uneven.
It would be desirable to have a blank construction free of these problems and yet economical and simple to manufacture, ship and store.